Fluid dispense pump with drip prevention mechanism and method for controlling same

ABSTRACT

A material dispensing pump includes a drip prevention system and method so as to avoid undesired dripping of the dispensed fluid. In one example, the fluid path is sealed. Positive pressure is applied to the fluid during a dispensing operation to present the fluid to the auger-style pump at a desired rate. Between dispensing operations, or when dispensing is completed, the fluid is placed in suspension, for example by applying a negative pressure, thereby preventing the fluid from being inadvertently released at the dispense tip. In addition, following a dispensing operation, the pump dispensing controller can be programmed to reverse the rotation of the feed screw, in order to draw the material in a reverse direction and to further suspend the fluid.

RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.13/534,703, filed Jun. 27, 2012, which is a continuation application ofU.S. Ser. No. 12/715,805, filed Mar. 2, 2010, now U.S. Pat. No.8,220,669, which is a continuation application of U.S. Ser. No.11/328,328, filed Jan. 9, 2006, now U.S. Pat. No. 7,694,857, which is acontinuation application of U.S. Ser. No. 10/424,273, filed Apr. 28,2003, now U.S. Pat. No. 6,983,867, which claims the benefit of U.S.Provisional Patent Application No. 60/376,536, filed Apr. 29, 2002, andis related to U.S. patent application Ser. No. 10/054,084, filed Jan.22, 2002, now U.S. Pat. No. 6,892,959, U.S. patent application Ser. No.10/038,381, filed Jan. 4, 2002, now U.S. Pat. No. 6,957,783, U.S. patentapplication Ser. No. 09/702,522, filed Oct. 31, 2000, now U.S. Pat. No.6,511,301 and U.S. patent application Ser. No. 09/491,615, filed Jan.26, 2000, now U.S. Pat. No. 6,547,167, the contents of each beingincorporated herein by reference, in their entirety.

BACKGROUND OF THE INVENTION

Contemporary fluid dispense systems are well suited for dispensingprecise amounts of fluid at precise positions on a substrate. A pumptransports the fluid to a dispense tip, also referred to as a “pin” or“needle”, which is positioned over the substrate by a micropositioner,thereby providing patterns of fluid on the substrate as needed. As anexample application, fluid delivery systems can be utilized fordepositing precise volumes of adhesives, for example, glue, resin, orpaste, during a circuit board assembly process, in the form of dots forhigh-speed applications, or in the form of lines for providing underfillor encapsulation.

Early dispensing pumps included a syringe with a dispense tip and apressured air/vacuum source. Air pressure was applied to a plunger inthe syringe, causing the plunger to engage a fluid in the syringe,thereby initiating a dispensing operation by forcing the fluid out ofthe dispense tip. To halt operation, a vacuum was drawn on the plunger.In this manner, dispensing operations were controlled by regulating theair pressure/vacuum applied to the syringe. While this embodiment wasadequate for certain applications, as technology evolved to demandedhigher dispensing accuracy, its application became somewhat limited.

Contemporary dispensing pumps improved capability by increasing controlover the timing and volume of the dispensing operation. This wasaccomplished through the integration of the feed screw into thedispensing pump system. Such systems comprise a syringe, a feed tube, adispense cartridge, and pump drive mechanism. The syringe contains fluidfor dispensing, and has an opening at its distal end at which a feedtube is connected. The feed tube is a flexible, hollow tube fordelivering the fluid to the cartridge. The cartridge is hollow andcylindrical and includes an inlet neck at which the opposite end of thefeed tube is connected. The inlet neck directs the fluid into thehollow, central cartridge chamber.

A feed screw disposed longitudinally through the center of thecylindrical chamber transports the fluid in Archimedes principle fashionfrom the inlet to a dispensing needle attached to the chamber outlet. Acontinuously-running motor drives the feed screw via a rotary clutch,which is selectively actuated to engage the feed screw and therebyeffect dispensing. A bellows linkage between the motor and cartridgeallows for flexibility in system alignment.

Pump systems can be characterized generally as “fixed-z” or “floating-z”(floating-z is also referred to as “compliant-z”). Fixed-z systems areadapted for applications that do not require contact between thedispense tip and the substrate during dispensing. In fixed-zapplications, the dispense tip is positioned and suspended above thesubstrate by a predetermined distance, and the fluid is dropped onto thesubstrate from above. In floating-z applications, the tip is providedwith a standoff, or “foot”, designed to contact the substrate as fluidis delivered by the pump through the tip. Such floating-z systems allowfor tip travel, relative to the pump body, such that the entire weightof the pump does not bear down on the substrate.

Such conventional pump systems suffer from several limitations. Themotor and rotary clutch mechanisms are bulky and heavy, and aretherefore limited in application for modern dispensing applicationsrequiring increasingly precise, efficient, and fast operation. Theexcessive weight limits use for those applications that require contactof the pump with the substrate, and limits system speed and accuracy,attributed to the high g-forces required for quick movement of thesystem. The mechanical clutch is difficult to control, and coasts to astop when disengaged, resulting in deposit of excess fluid. Clutchcoasting can be mitigated by a longitudinal spring mounted about thebody of the feed screw and urged against the chamber end to offerrotational resistance. However, the spring adds to the length of thecartridge, and contributes to system complexity.

The inlet neck feeds directly into the side of the feed screw or“auger”. Consequently, as the auger collects material from the small andcircular inlet port, high pressure is required for driving the materialinto the auger body, because the auger threads periodically pass infront of the feed opening, preventing material from entering. This leadsto inconsistent material flow. Additionally, the inlet neck is commonlyperpendicular to the auger screw, requiring the fluid to make a 90degree turn upon entering the pump. This further limits material flowand can contribute to material “balling” and clogging.

Overnight storage of dispensed fluids often requires refrigeration ofthe fluid and cleaning of the system. The syringe is typically mounteddirectly to a mounting bracket on the pump body such that the outputport of the syringe passes through an aperture on the mounting bracket.The feed tube is then coupled to the output port on the opposite face ofthe bracket. Since the tube and bracket are on opposite sides of thebracket, removal of the syringe from the pump body requires dismantlingof the tube and syringe, which can contaminate fluid material positionedat the interface during disassembly. Further, since the syringe andcartridge can not be removed and stored together as a unit, disassemblyand cleaning of the cartridge is required. Additionally, the inlet neckis narrow and therefore difficult to clean.

Dispense pumps are commonly mounted on a positioning platform, or gantrysystem, that positions the pump along the Cartesian x, y and z axes,relative to the substrate. A computer, or controller, performs variousdispensing tasks using the positioning platform to control the pumpposition according to commands that are programmed by an operator. Asexplained above, pump/platform systems currently in use in the fieldemploy the aforementioned brush motor or clutch-based pumps. Such pumpsoperate in response to a time-period-based signal from the controller,the duration of which dictates the length of time the motor is on (or,for a continuously-running motor system, the length of time the clutchis engaged), and therefore the amount of fluid that is dispensed. Forexample, the rising edge of the signal may initiate rotation of thebrush motor (or engage the clutch), and the falling edge may turn offthe motor (or disengage the clutch). While such pumps are adequate foroperations requiring relatively large dispensing volumes, at smallervolumes the system resolution is relatively limited, since the timingsignal is relatively inaccurate at shorter time periods, and sinceresidual motion in the clutch or brush motor is difficult to predict.Assuming the platform/pump controller to be a computer-based system, thetime-period-based signal may be subject to even further variability,since initiation of the signal may be delayed while other tasks areprocessed by the computer.

Conventional dispensing pumps are further limited in that following adispensing operation, or in between dispensing operations, material cancontinue to flow, or drip, from the pump and dispense tip. This can leadto excessive dispensing of the fluid, for example in the form of greaterdispensed fluid volume than desired, or the dripping of fluid atundesired locations on the substrate. This is especially problematic fordispensing of materials of relatively low viscosity, which tend to flowor drip more freely.

Others have attempted to address this problem, with limited success. Forexample, U.S. Pat. No. 5,819,983 proposes a pump embodiment having aauger screw that is axially moveable between a flow position, in whichmaterial is permitted to flow through the outlet, and a sealed position,in which material is prevented from flowing. A pneumatic system is usedto drive the screw downward and upward between the flow position and thesealed position. This system is however mechanically complex, owing tothe number of moving parts, and can cause eventual wear on the inlet ofthe dispensing needle, where the auger screw comes in contact with theneedle when in a sealed position. In addition, the vertical position ofthe auger must be set, which can further complicate setup andmaintenance of the system. Wear and improper settings can lead toinaccurate volume dispensing, and mechanical complexity can lead tojamming.

SUMMARY OF THE INVENTION

The present invention is directed to a fluid pump and cartridge systemthat overcomes the limitations of conventional systems set forth above,by providing a pump that includes a drip prevention mechanism and amethod of operating the same that mitigate or prevent undesired releaseof the dispensed fluid. In one example, the fluid path is sealed.Positive pressure is applied to the fluid during a dispensing operationto present the fluid to the auger-style pump at a desired rate. Betweendispensing operations, or when dispensing is completed, the fluid isplaced in suspension, for example by applying a negative pressure,thereby preventing the fluid from being inadvertently released at thedispense tip. In addition, following a dispensing operation, the pumpdispensing controller can be programmed to reverse the rotation of thefeed screw, in order to draw the material in a reverse direction and tothereby further suspend the fluid.

In one embodiment, the present invention is directed to a materialdispensing pump comprising a feed screw including a helical feed pathdefined between a major diameter and a minor diameter of the feed screw;the feed screw being driven in a first direction of rotation during adispensing operation of material to be dispensed. A feed screw housingincludes a cavity, the feed screw extending through the cavity. The feedscrew housing further includes an inlet port and an outlet port incommunication with the cavity, the helical feed path being substantiallysealed from ambient air between the inlet port and the outlet port. Apressure unit applies positive pressure to cause material to bepresented to the inlet port at a desired rate during a dispensingoperation such that the material flows through the helical feed pathtoward the outlet port. A material suspension unit places the materialin suspension following the dispensing operation.

In one embodiment, the material suspension unit applies negativepressure to the material to place the material in suspension. In anotherembodiment, the material suspension unit comprises means forconstricting the material flow path, such as rollers or pinchers.

A material reservoir is in communication with the inlet port, thematerial reservoir containing the material to be dispensed during thedispensing operation. A feed tube is coupled between the materialreservoir and the inlet port. The feed tube may be formed of anelastically compressible material and means may be provided forconstricting the feed tube to place the material under suspension.

The material reservoir, in one embodiment, comprises a syringe, in whichcase, the positive pressure is applied to a plunger of the syringe. Thepositive pressure may comprise pumped air provided by the pressure unitand applied to the plunger, and the negative pressure may comprise avacuum provided by the pressure unit and drawn on the plunger.

A motor may be coupled to the feed screw for driving the feed screw inthe first direction of rotation during a dispensing operation. The motorfurther drives the feed screw in a second direction of rotation oppositethe first direction following the dispensing operation. The movement ofthe screw in the second direction operates in conjunction with thenegative pressure to suspend the flow of material. The motor maycomprise a closed-loop servo-motor.

The feed screw includes a cylindrical neck, in which case the sealcomprises an O-ring about the neck between the neck and the feed screwhousing. The feed screw has a longitudinal axis, and the inlet port iselongated in a direction along the longitudinal axis of the feed screw.

In another embodiment, the present invention is directed to a method fordispensing material. During a dispensing operation of material to bedispensed, a feed screw including a helical feed path is driven in afirst direction of rotation, the feed screw being disposed in a cavityof a feed screw housing such that the helical feed path is substantiallysealed from ambient air. Positive pressure is applied to the material tocause material to be presented to the helical feed path at a desiredrate. Following the dispensing operation, the material is placed undersuspension.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the more particular description ofpreferred embodiments of the invention, as illustrated in theaccompanying drawings in which like reference characters refer to thesame parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIGS. 1A and 1B are an exploded perspective view and an assembledperspective view respectively of a pump assembly configured inaccordance with the present invention.

FIGS. 2A and 2B are an exploded perspective view and an assembledperspective view respectively of a fixed-z-type cartridge assembly inaccordance with the present invention.

FIGS. 3A and 3B are an exploded perspective view and an assembledperspective view respectively of a floating-z-type cartridge assembly inaccordance with the present invention

FIGS. 4A, 4B and 4C are side views of a cartridge opening illustratingthe conventional embodiment having a small, circular opening, and firstand second embodiments of the present invention having elongatedopenings respectively.

FIG. 5A is a cutaway side view of a cartridge feed mechanism employing acarbide liner including an elongated slot at the inlet to allow forincreased capturing of input material at the feed screw inlet, in orderto promote consistency in material flow at a reduced pressure, inaccordance with the present invention. FIG. 5B is a perspective view ofthe liner having an elongated slot, in accordance with the presentinvention.

FIGS. 6A and 6B illustrate operation of the syringe and cartridge quickrelease mechanisms, in accordance with the present invention.

FIGS. 7A, 7B and 7C illustrate side, front, and top views respectivelyof a quick-release mounting plate, for mounting the pump to a pumpdispensing frame, in accordance with the present invention.

FIG. 8 is a illustration of an improved dispensing configurationemploying a vacuum tube inserted into the material feed tube, inaccordance with the present invention.

FIG. 9 is an illustration of an air purge configuration wherein a purgevacuum is applied to the needle assembly for initially purging thematerial flow of air pockets, to prime the system for dispensing, inaccordance with the present invention.

FIG. 10 is an illustration of a bellows configuration for application tothe top of a material feed syringe, allowing for use of minimal pressureto drive material flow with mitigation or elimination of air migrationinto the material, in accordance with the present invention.

FIG. 11 is a cutaway side view of a dispense tip configuration inaccordance with the present invention.

FIGS. 12A and 12B are side and end views respectively of the dispensetip of FIG. 11 having a vented outlet, in accordance with the presentinvention.

FIGS. 13A and 13B are side and end views respectively of the dispensetip of FIG. 11 having a vented and relieved outlet, in accordance withthe present invention.

FIGS. 14A and 14B are side and end views respectively of the dispensetip of FIG. 11 having a vented and beveled outlet, in accordance withthe present invention.

FIG. 15 is a closeup end view of an outlet vent, in accordance with thepresent invention.

FIG. 16 is a block diagram of a control system for the pump of thepresent invention.

FIG. 17 is a cross-sectional view of a dispensing pump having dripprevention capability in accordance with the present invention.

FIGS. 18A and 18B are cross-sectional closeup views of the dispensingpump of FIG. 17, illustrating the operation of the induced vacuum andthe reverse motion of the auger screw, in accordance with the presentinvention.

FIGS. 19A and 19B are side conceptual views of a mechanism for pinchingthe feed tube, in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A and 1B are an exploded perspective view and an assembledperspective view respectively of a pump assembly configured inaccordance with the present invention. With reference to FIGS. 1A and1B, an embodiment of the dispensing pump 18 comprises a motor 42, anoptional transmission box 44, a pump housing 52, and a cartridge 58.

The motor 42 preferably comprises a closed-loop servo motor with anindependent motion controller 43. The motion controller 43 may beprovided by the host dispensing platform, and may comprise, for example,a Delta Tau controller, Northbridge, Calif., USA. The closed-loop servomotor may comprise, for example, a Sigma Mini Series motor, produced byYaskawa Electric Corp., Japan. Feedback is preferably provided by arotary encoder, for example providing 8192 discrete counts over 360degree rotation. The motor 42 includes an axle 41 which operates todrive the feed screw in the cartridge assembly 58 (described below). Inthis manner, high-performance control is maintained over materialdispensing. For example, rotary position, rotational velocity, andacceleration/deceleration of the feed screw can be readily controlled bythe closed-loop servo motor, and is easily programmed at the controller43. This is compared to conventional embodiments that rely on timedopen-loop coasting of a mechanical clutch for control over the feedscrew. Additionally, the closed-loop servo-motor is generally a compactsystem that is small, lightweight, and designed for high-performanceoperation; as compared to the bulky, inefficient, and inaccurateconventional motor pump systems.

An optional planetary-gear transmission box 44 may be provided to stepdown the available motor positions, thereby providing even more enhancedcontrol over angular position of the feed screw. For example, step-downtransmissions offering 7:1, 25:1, and 48:1 step-down ratios areavailable for increasing the number of angular steps from 8,192 to57,344, 204,800 and 393,216 respectively, depending on the application.Such transmission boxes are also available in compact units that matchwell in size and weight with the closed-loop servo motor 42.

The pump housing 52 comprises a machined or die-cast body having anopening 49 at a top portion for receiving the motor drive axle 41 oroptional transmission box 44 drive axle (not shown). The interior of thehousing 52 is hollow for receiving a cartridge 58 that extends throughthe housing 52 from an opening 51 at a bottom portion, upward to the topportion, and interfaces with the motor drive axle or transmission boxdrive axle. The motor 42 and transmission box 44 are mounted to eachother, and to the housing 52, by bolts 46, and screws 24, 28, and 30.Cavities 53 are preferably provided in the walls of the housing 52, inorder to reduce weight.

A cartridge release lever 34 is rotatably mounted to the housing 52 bybolt 38. When rotated, the cartridge release lever 34 engages anactuator pin 56, biased by spring 54 to remain in a released position.With reference to FIGS. 6A and 6B, the actuator pin 56 extends into thebody of the housing 52 and engages an actuator pin capture 62 (see FIG.2B) or elongated actuator pin capture (see FIG. 3B) formed in thecartridge body 60. In this manner the cartridge release lever isoperable to remove/insert a cartridge 58 at the underside of the housing52 as indicated by arrow 95 (see FIG. 1B).

A syringe 22 and feed tube 40 are releasibly coupled to a side wall ofthe housing, as shown. The syringe 22 includes a syringe holder 20, asyringe body 22, and a threaded outlet 23. An outlet adapter 32 mateswith the thread 23 at an inlet end and with feed tube 40 at an outletend. The feed tube 40 is preferably formed of a flexible material, afirst end of which elastically deforms to fit over the outlet end of thesyringe outlet adapter 32 to form a tight seal at neck region 33. Thesecond end of the feed tube 40 inserts into a feed aperture 64 (seeFIGS. 2B and 3B) formed in the cartridge body 60, or alternatively mateswith a cartridge inlet port extending from the cartridge body 60.

With reference again to FIGS. 6A and 6B, the syringe 22 is likewisepreferably configured to be readily separable from the pump housing 52,along with the cartridge 58. To accommodate this feature, a syringequick-release arm 48 extends from a side wall of the pump housing 52,and includes a slot for snap-capturing the neck region 33 of the syringeoutlet adapter 32. The quick release arm preferably elastically deformsto receive the neck 33, and to fix the syringe 22 in position during adispensing operation. In this manner, the cartridge release lever 34operates in conjunction with the syringe quick release arm to allow foreasy removal and storage of the cartridge mechanism 58 and syringe 22 asa unit. This is especially helpful in situations where overnightrefrigeration of the dispensing material is required, since the entirematerial pathway can be removed and stored as a unit, without the needfor disassembly and cleaning of the individual components, as requiredby conventional pump configurations.

A release bracket 50 is mounted to a side wall of the housing 52. Withreference to FIGS. 7A and 7B, the release bracket 50 includes first andsecond alignment pins 110 and a central lock pin 114, including a body111 and retaining head 112, extending outwardly from its surface. Acorresponding release bracket plate 124 is mounted to a dispensing frame122, and includes alignment pin captures 116, a lock pin capture 118 anda spring-loaded lever 120. When operated, the lever, engages/disengagesa clasp within the lock pin capture 118, that, in turn, clasps theretaining head 112 of the release bracket, when inserted and properlyaligned with the plate 124. In this manner, the pump 18 can be readilyattached/detached from the pump dispensing frame for maintenance andinspection. The alignment pins 110 and/or lock pin body 111 or retaininghead 112 may optionally be keyed to ensure proper engagement. As shownin the top view of FIG. 7C, the release bracket plate 124 may optionallybe configured with side walls 125 that communicate with the outer edgeof the release bracket in order to provide a lateral keying function,thereby ensuring alignment accuracy and strength in cooperation with thealignment pins 110.

FIGS. 2A and 2B are an exploded perspective view and an assembledperspective view respectively of a fixed-z-type cartridge 58 assembly inaccordance with the present invention. The cartridge assembly includesan elongated cartridge body 60, a first end of which is adapted toreceive a fixed-z-type dispensing needle, for example Luer™-style needle68. An opening at a second end of the cartridge receives an auger screw,or feed screw 74 having threads 75 at a first end, and having an indexedshaft 66 at an opposite end, adapted to register with the motor axle 41,or transmission axle. The auger screw 74 includes a collar 78, theheight of which is adjustable by set screw 76. Washer 72 ensures a tightseal. A cap nut 80 contains the various cartridge components within thecartridge body 60. As explained above, an inlet port 64 is formed in thebody 60 of the cartridge for receiving an end of the feed tube, for thedelivery of material toward the feed screw threads 75. An actuator pincapture 62 engages the cartridge release pin 56, as described above. Inthe fixed-z embodiment of FIGS. 2A and 2B, the actuator pin capture 62is the size of the release pin, to prevent longitudinal travel of thepump.

FIGS. 3A and 3B are an exploded perspective view and an assembledperspective view respectively of a floating-z-type cartridge 58 assemblyin accordance with the present invention. In this embodiment, the feedscrew mechanism is similar to that of FIGS. 2A and 2B; however, thecartridge is adapted for receiving a floating-z-type dispensing needle82. The needle body 82 registers with locator 88 at the cartridgeoutlet, and is fixed in place by needle nut 84. For the floating-z-typecartridge assembly, an elongated actuator pin capture 86 is provided toallow for longitudinal travel of the cartridge 58 relative to the pumphousing 52 during a dispensing operation.

FIG. 4A of a inlet port for a conventional cartridge 108 embodimenthaving a small, circular port opening 106. In this embodiment, it can beseen that the pressurized material entering the port opening 106periodically confronts a major diameter of the feed screw thread 102,which periodically inhibits flow of material into the feed screw cavityformed between the minor diameter portion 104 of the thread and theinterior wall of the cartridge body 108. As much as ⅓ to ½ of the portopening can be periodically blocked by the major diameter of the feedscrew thread 102 at any given time. The blockage fluctuates as afunction of the rotational position of the feed screw which can causeinconsistency in material dispensing, especially at small tolerances,and can further alter pressure in the syringe system, as the blockagerestricts material flow. The blockage further increases the likelihoodof material stagnation and drying at the inlet port, in turn causingsystem contamination.

The present invention overcomes this limitation by providing anelongated cartridge inlet port. With reference to FIGS. 4B and 4C, theelongated inlet port 100 of the present invention is preferablyelongated in a longitudinal direction, with respect to the longitudinalaxis of the feed screw 74. In this manner, dispensing material ispresented to a larger portion of the feed screw cavity formed betweenthe minor diameter portion 104 and the inner wall of the cartridge 70.This configuration reduces pressure requirements for material deliverythrough the system, and enhances consistency in material flow, as thedependency on material flow rate as a function of the feed screw threadposition is mitigated or eliminated. In general, a longer inlet port asshown in FIG. 3 is preferred, as compared to the relatively shorterinlet port 100 shown in FIG. 4B; however, the inlet port 100 should notbe so long as to provide an opportunity for pooling of dormant materialin the inlet port 100 prior to flow through the feed screw 74.

FIG. 5A is a cutaway side view of a cartridge feed mechanism employing acarbide liner 70 including an elongated slot 100 at the inlet port toallow for increased capturing of input material at the feed screw inlet,in order to promote consistency in material flow at a reduced pressure,in accordance with the present invention. FIG. 5B. is a perspective viewof the liner having an elongated slot, in accordance with the presentinvention.

In this embodiment, the elongated inlet port is provided by a slot 100formed in a side wall of a cylindrical carbide liner 70 inserted in thecartridge body 60 about the feed screw 74. The cartridge inlet port 64comprises a standard circular bore formed in the cartridge body 60,preferably at an acute angle relative to the feed screw 74, to allowgravity to assist in material flow. An elongated chamber, or pocket 101,is formed within the slot 100, between the feed screw 74 and the innerwall 103 of the cartridge body, in a region proximal to the inlet port64. The elongated pocket 101 allows for dispensing fluid to migrate in adownward direction, and is captured by the feed screw threads over alarger surface area, conferring the various advantages outlined above.

FIG. 8 is a illustration of an improved dispensing configurationemploying a vacuum tube inserted into the material feed tube. In thisembodiment, entrapped gas impurities, such as air microbubbles, aredrawn from the material supply during a dispensing operation, therebypurging the system of entrapped air. A vacuum unit 126 draws a vacuumfrom the material supply tube 40, for example by a vacuum tube 127 withneedle 128 inserted into the material feed tube 40, along the directionof material flow, as shown. In this manner, air is withdrawn from thedispensed material, leading to an improvement in dispensing consistency,especially at small tolerances.

FIG. 9 is an illustration of an air purge configuration wherein a purgevacuum is applied to the needle assembly for initially purging thematerial flow of air pockets, to prime the system for dispensing. Inthis process a first purge interface 134 is placed on the end of thefeed tube, and a vacuum is drawn by vacuum unit 126, thereby purging thefeed tube 40 of entrapped gas. A second purge interface 134 is thenplaced on the cartridge body outlet 133 while the feed screw is rotatedslowly until material presents itself at the outlet 133. A vacuum isdrawn by vacuum unit 126 to eliminate entrapped gas from the cartridge.A third purge interface 134 is then placed on the needle assembly 82 anda vacuum is drawn by vacuum unit 126 to eliminate entrapped air from theneedle body. Entrapped air is thus substantially removed from the feedtube, auger screw and dispensing needle. Normal dispensing can commencefollowing removal of the purge interface. Note that the first, secondand third purge interfaces 134 may require different interfaceconfigurations for the different components undergoing purging.

FIG. 10 is an illustration of a bellows configuration for application tothe top of a material feed syringe, allowing for use of minimal pressureto drive material flow with mitigation or elimination of air migrationinto the material. In this configuration, a bellows means 130, forexample comprising an air-tight, flexible material, is inserted at thepiston end of, and replaces the piston of, a dispensing syringe 22. Thebellows is pressurized by air pressure unit 132 from within and expands,thereby exerting pressure on the underlying material 135, forcingmaterial flow through the outlet 32. In this manner, material can bedriven with minimal pressure, and with minimal air migration into thematerial, as compared to plunger-style drivers. In a preferredembodiment, the bellows comprises a latex film applied about the lip ofthe syringe top. The flexible latex film serves to conform to the innerwalls of the syringe during expansion, pushing the underlying materialin a downward direction The syringe top is preferably vented to allowfor expansion of the bellows.

In this manner a high-performance, lightweight pump configuration isprovided. The pump is operable in both fixed-z and floating-z mode.Quick release mechanisms provide for storage of the syringe andcartridge as a single unit, without the need for component disassembly.The components themselves are relatively easy to clean and maintain. Theelongated inlet port provides for enhanced dispensing consistency at alower material pressure, while the various purging and primingtechniques allow for removal of entrapped gases, further improvingdispensing consistency.

The pump of the present invention is amenable to use with dispense tipsconfigured in accordance with those described in U.S. patent applicationSer. No. 09/491,615, filed Jan. 26, 2000, the contents of which areincorporated herein by reference, in their entirety.

With reference to FIG. 11, such dispense tips 200 include a bore 210formed in the neck 202 of the dispense tip 200, the bore 210 having aninput end 211 of a first inner diameter D1, an output end 208 of asecond inner diameter D2, and an inner taper 212 for transitioning theinner surface of the bore from the first inner diameter D1 to the secondinner diameter D2. This dispense tip configuration allows for thedelivery of fluid to the outlet 214 at a relatively low pressure ascompared to conventional dispense tips having a single, narrow, innerdiameter over the length of the neck. The wider diameter D1 along themajority of the neck 202 allows for delivery of fluid to the narrowdiameter D2 opening at a relatively low pressure that is more desirablefor volume control, while the relatively small opening 214 at the outputend 208 allows for control over the volume of the dispensed fluid on thesubstrate.

In particular, the pump of the present invention is amenable tooperation with dispense tips having a vented outlet face, as illustratedin FIGS. 12-15. Such vented dispense tips are beneficial in applicationswhere a pattern of dispensed fluid, such as an “X”, or a star-shapedpattern, is desired. Such applications include providing a fillet on asubstrate for adhering a circuit die to the substrate. As the area ofcircuit dies continues to decrease, there is an increasing need foraccurate dispensing of fillet patterns. An accurate and consistentdispense of the fillet pattern requires a predictable volume ofdispensed fluid, as well as a precise pattern shape. For example, it isdesirable that the legs of the X-pattern do not merge into one anotherdue to migration of fluid between the vents.

With reference to the cutaway side view of FIG. 12A and the output endview of FIG. 12B, in one embodiment, the vented dispense tip, configuredin accordance with FIG. 11, includes vents 216 (in this example, fourvents, but other numbers of vents are possible) that extend radiallyfrom the outlet 214 at the output end. The outer face 216 of the outputend is flat and has a diameter equal to that of the outer diameter ofthe neck of the dispense tip.

In the example of FIGS. 13A and 13B, the vented dispense tip, configuredin accordance with FIG. 11, includes vents 218 that extend radially fromthe outlet 214 of the output end. The outer face 216 of the output endis flat and has a diameter that is less than that of the outer diameterof the neck of the dispense tip, as a circular relief 220 is formedabout the outer face 216. The relief 220 is advantageous for thoseapplications that require presentation of the dispensed pattern at aposition close to an edge of a feature, or within a pocket on thesubstrate, since, owing to the relief 220, the center of the outlet 214can be positioned closer to the edge of the feature for a deposit offluid.

In the example of FIGS. 14A and 14B, the vented dispense tip, configuredin accordance with FIG. 11, includes vents 218 that extend radially fromthe outlet 214 of the output end 208. The outer face 216 of the outputend is flat and has a diameter that is less than that of the outerdiameter of the neck of the dispense tip. A bevel 222 is formed aboutthe outer face 216. In one example, the bevel can be formed according tothe techniques described in U.S. patent application Ser. No. 09/491,615,filed Jan. 26, 2000, the contents of which are incorporated herein byreference above. The bevel reduces surface tension between the depositedfluid and the dispense tip, leading to more consistent and predictabledeposit on the substrate. In an embodiment where the dispense tip bevel222 is ground in a longitudinal direction, i.e. in a direction parallelto the longitudinal axis of the neck, the resulting tooling scars arelongitudinal, and surface tension during a deposit is reduced evenfurther, as described in the referenced patent application.

With reference to the closeup view of FIG. 15, which illustrates anendwise view of a preferred embodiment of the dispense tip vent 218, thevent 218 preferably includes first and second angled faces 218A, 218Bthat are disposed at a vent angle θ with respect to each other. Deepervent pockets tend to leave material on the dispense tip following adeposit, since the surface tension is increased owing to the increasesurface area of the pocket. Rectangular, three-faced pockets having twoside walls and a ceiling suffer from this limitation. A preferredembodiment of the present invention therefore incorporates vents thathave two inner walls disposed at a vent angle θ to one another, as shownin FIG. 15. In one example, a 100 degree vent angle θ was found suitablefor permitting adequate material flow through the vent, while minimizingsurface tension at the outlet face 216. Other angles may be appropriate,for example between a range of 45 and 135 degrees; the selected angledepending on various characteristics of the deposit process, includingflow rate, material type, volume, and other considerations.

In a preferred embodiment, the outlet face 216, including the vents 218can be provided with a nutmeg-chrome finish, which provides anickel/Teflon™ plating on the outer surface. Such a finish serves tofurther reduce surface tension at the outlet face.

In the closed-loop servo motor pump configuration of the presentinvention, auger rotation is controlled over its entire motion, frominitiation to completion of a dispensing operation. In view of this, thecontrol system managing the operation of the auger rotation is incomplete control of the angular velocity and angular acceleration of theauger as it rotates. By managing the velocity, the dispensing of fluidcan be controlled to an exceptionally high degree, including not onlyvolume, but also rate. This, in turn, allows for predictability in fluidmigration through the vents of the vented dispense tip during a deposit.

For example, assuming the rate of deposit is too slow, the dispensedmaterial will tend to flow through the path of least resistance. If oneof the vents has lower material flow resistance than the others, thiscan lead to an imbalanced dispense pattern, with more fluid deposited inthe less-resistant leg. However, with control over the velocity of theauger, as in the configuration of the present invention, the velocitycan be increased, causing the material to flow down all legs at aconsistent rate, leading to more reliable deposit pattern profiles.

In an embodiment where the vents 218 are machined in the outlet face ofthe dispense tip, the vents are preferably ground or formed to havetooling lines in a direction parallel to the long axis of the vents, inorder to reduce surface tension. The configuration of the vent dependson the width and volume of the desired dispense pattern.

Using the vented dispense tips illustrated above, a range of dispensepatterns can be created. For example, assuming the auger is caused torotate slightly, a small dot can be formed on the substrate, since fluidmigration up the vents does not take place. With further rotation of theauger, an X pattern can be formed having legs of a length less than thelength of the vents, since fluid migration takes place for a portion ofthe vents. With even further rotation of the auger, the X pattern can beformed with longer legs that equal the length of the vents. In thismanner, a single, vented dispense tip, in combination with the closedloop servo motor dispense pump of the present invention can provide arange of dispensing profiles while reducing the number of dispense tipsrequired.

The outlet face 216 effectively serves as a foot for the dispense tip.In this manner, the vented dispense tip of the present invention issuitable for floating-z applications, wherein the outlet face comes incontact with the substrate during a dispensing operation. Alternatively,the vented dispense tip of the present invention is also applicable tofixed-z configurations.

FIG. 16 is a block diagram of a control system which permits thedispensing pump of the present invention to be operated in conjunctionwith a conventional pump position controller. The control systemincludes a dispensing pump 18, a position controller 310, and adispensing controller 300.

The pump 18 preferably comprises a dispensing pump driven by aclosed-loop servo motor 42 having indexed rotational, or angular,positions, for driving an auger screw for delivery of fluid to thedispense tip. As explained above, the motor 42 preferably includes anencoder that provides for precise control over the angular positioningof the motor during operation. To accommodate this, the motor 42receives control signals 309 from the dispensing controller 300. Thecontrol signals 309 may comprise, for example, digital signals forcontrolling the angular, or rotational, position, the angular velocity,and/or the angular acceleration of the motor 42.

The pump 18 is mounted to a conventional pump gantry 314 that operatesin conjunction with a gantry controller 312 to comprise the positioncontroller 310. The position controller 310 may comprise a conventionalpump dispensing platform designed for use with a conventional brushmotor or clutch-based pump. The present invention therefore allows forthe inventive pump 18 described above to be compatible with theconventional position controllers 310, thereby allowing for reversecompatibility with conventional dispensing platforms, or gantry systems,currently in use in the field, but limited by the conventionalbrush-motor or clutch-based pumps, for which their use was designed.

In the conventional position controller 310 system, the gantrycontroller 312 is programmable and generates positioning signals 313 formoving the pump gantry 314 into position along Cartesian axes (x, y, z).Upon determining that the pump gantry 314 is in position for adispensing operation, the gantry controller 312 generates a motoractivation signal 316 comprising a rectangular waveform having a risingand falling edge, the time period between the edges dictating the lengthof time that the motor operates (or for a continuously-running motor,the length of time the clutch is engaged), and therefore the amount offluid that is dispensed.

The pump 18 of the present invention however includes a moresophisticated, position-based motor that is based on an indexing, orcount, signal protocol, rather than a time-based protocol. Toaccommodate this, the system of the present invention includes adispensing controller 300 that generates a position-based pump controlsignal 309 for the motor 42 in response to the time-based motoractivation signal 316 generated by the gantry controller 312 of theconventional position controller 310. In this manner, the dispensingcontroller 300 of the present invention allows for the pump 18 of thepresent invention to be used in conjunction with a conventional positioncontroller 310.

As described above, during a pump operation, the position controller 310positions the pump gantry 314 according to program coordinates alongCartesian axes 313. Upon determining that the pump gantry 314 is inposition for dispensing operation, the gantry controller 312 initiates amotor activation signal 316. The motor activation signal 316 comprises arectangular waveform that may be, for example, active-high oractive-low. For purposes of the present invention an active-high signalwill be assumed. The motor activation signal 316 is received by aninterface board 304 which converts the rectangular waveform of the motoractivation signal to a digital signal 305 that is consistent with theprotocol for programming the pump motion control card 306, for examplethe Delta Tau controller referenced above. The controller 306 includesan amplifier 308 for driving the dispense signals 309 over a cableinterface to the motor 42. The motor 42 receives the converted dispensesignals 309 and responds by performing a dispensing operation inaccordance with the signals 309. In general, dispensing operations canbe categorized according to dot dispensing and line dispensing.

In a dot dispensing operation, the position controller 310 moves thepump gantry 314 to a fixed position and initiates a brief motoractivation signal 316 having a short period designed to activate theconventional motor for a brief time period so as to dispense a singledot on the substrate. Since the pump gantry 314 is stationary during thedispensing operation, a dot is dispensed on the substrate, the volume ofwhich depends on the period of the rectangular motor activation signal316. The interface board 304 of the dispensing controller 300 interpretsthe rising edge of the motor activation signal 316 as an indication thatthe pump gantry 314 is in position and, in response, commences adispensing operation. In a preferred embodiment, the dispensingcontroller 300 is programmed to be synchronized with the program of theposition controller 310 such that both controllers 300, 310 are aware ofthe type of operation being performed, for example a dot, or line,dispensing operation. Assuming a dot dispensing operation, thedispensing controller 300 responds to the rising edge of the motoractivation signal 316 by generating an dispense signal 309 that informsthe motor 42 of the number of indexed rotational position counts thatthe motor is to traverse during the dispensing operation. The dispensesignal 309 allows for optional further sophistication in control overthe motor. For example, the dispense signal 309 may also includeinformation related to the angular velocity and angular acceleration ofthe motor 42 during the dispensing operation. At completion of thedispensing operation, the interface board 304 of the dispensingcontroller 300 optionally generates a feedback signal 318 to indicatethat the dispensing operation is complete. Certain position controllers310 utilize such a feedback signal 318 to indicate that the dispensingoperation is complete and that the gantry controller can now advance thepump gantry 314 to the next position for dispensing. Assuming theposition controller 310 does not accommodate such a feedback signal,then the position controller 310 should allow for a sufficient timeperiod to a lapse following a dispensing operation to ensure that thedispensing operation has been completed by the dispensing controller 300before advancing to the next dispensing activity.

In a line dispensing operation, the dispensing controller 300 receivesthe leading edge of the motor activation signal 316 at the interfaceboard 304 and instructs the pump motion control 306 via signal 305 togenerate a dispense signal 309 that programs the motor 42 to activate,and hold at a constant angular rate, for a period of time that isconsistent with the duration of the motor activation signal 316. Duringline dispensing, the pump gantry 314 is in motion while the pump motor42 is dispensing. The combination of the motion of the pump gantry 314and the rotation of the motor 42 results in line-patterns beinggenerated on the substrate. At the falling edge of the motor activationsignal 316, the dispensing controller 300 modifies the dispense signal309 to halt the rotation of the motor 42, thereby completing the linedispensing operation. As explained above, the dispense signals 309 mayfurther optionally vary the angular velocity and/or angular accelerationof the motor 42 during a line dispensing operation.

In a preferred embodiment, the dispensing controller 300 isprogrammable, for example via a touch screen interface 302, or astandard computer interface, for recording a plurality of dispensingoperations in automated fashion in conjunction with the programmableposition controller 310. The program may comprise a single, repetitiveoperation or multiple, programmable operations wherein the position,velocity, and acceleration of the motor 42 are programmable at each dotor line dispensing operation step. The user interface 302 may furtherallow for manual control over the dispense pump 18, or automatic controlbased on the motor activation signal 316 received from the positioncontroller 310. The user interface further preferably allows for safestorage of programs and automatic retrieval of programs, for exampleaccording to program titles, or part numbers.

In preferred embodiments, the user interface further includes reversemode control for operating the motor in reverse rotation, and a purgemode which allows for continuous rotation of the motor 42 in a forwarddirection for a length of time to be controlled by the user at the userinterface 302, or optionally at the position controller 310.

In this manner, the dispensing controller 300 of the present inventionallows for the advanced pump 18 of the present invention to bereverse-compatible with conventional position controllers 310.

FIG. 17 is a cutaway side view of a dispensing pump configuration inaccordance with the present invention. In this configuration, the pumpis provided with drip prevention capability in order to avoidover-dispensing of fluid at a given location, or to avoid dripping offluid between dispensing operations at undesired locations.

The configuration of FIG. 17 includes a material dispensing container430 or reservoir, for example in the form of a syringe, driven by an airpressure/vacuum unit 402, and a fluid dispensing pump 432. The pump 432is of the auger-screw Archimedes-style pump described above. In the pump432, the auger screw shaft 66 extends longitudinally through the body ofthe pump as shown, and is driven by a motor, as described above.

The path of the material 436 being dispensed begins in the dispensingcontainer 430. In this example, the container comprises a syringe 22having a plunger 410. The volume of air 440 above the plunger is sealedby syringe cap 411, and has a pressure value, for example, positive,negative, or zero, pressure, that is controlled by the airpressure/vacuum unit 402. Under positive air pressure applied to theplunger 410, for example ranging from 1-10 psi, fluid material isdispensed from the syringe at outlet 32 and through feed tube 40, and isintroduced into the body of the pump cartridge 60, at port 100 asdescribed above at a desired rate, for example such a rate as to avoidcavitation of the dispensed material. An elongated inlet port 100 forintroducing the material to the feed screw is preferred, as describedabove. The material flows thorough the inlet port 100, where itinterfaces with a side portion of the feed screw 74. Rotation in thefeed screw 74 in the first clockwise direction 408, induced by motor 42,as described above, propels the material in a downward direction towardthe dispense tip 82 outlet port. The rotation of the auger screw 74, incombination with the positive air pressure generated at the airpressure/vacuum unit 402 and operating on the plunger 410, causesmaterial to be dispensed at the dispense tip 82 in metered fashion, asdescribed above. A suitable pressure level is determined based on manyfactors, including the viscosity of the fluid, the volume of thereservoir, the width and length of the feed path, and the like. Too muchapplied pressure would overcome the auger metering capability and wouldpush material through the screw; too little applied pressure would causevoids to appear in the dispensed material.

An air seal, for example, in the form of an O-ring 412, is providedabout an upper portion of the neck, or body, of the rotatable augerscrew shaft 66 in order to form an airtight seal at the top portion ofthe material flow path in the cartridge 70. The O-ring preferably allowsfor free rotation of the shaft 66 therein, while providing asubstantially air tight seal therewith. The O-ring may be formed, forexample, of a Viton™ material, or silicone rubber material, and ispositioned by a containment washer 414, which, in turn, is secured by anauger collar 416 and a threaded spanner nut 418. In this manner, thematerial path is sealed along the path from the plunger 410 to thematerial inlet port 100, to the dispense tip 82 outlet port of the pump432. The seal operates to prevent ambient air external to the pump bodyfrom compromising the positive or negative pressure applied to thematerial by the plunger 410 and air pressure/vacuum unit 402.

With reference to FIG. 18A, following a dispensing operation, material420 is present at the outlet of the dispense tip 82. As described above,this material 420 can become dislodged from the dispense tip at anundesired time subsequent to the dispensing operation, leading todispensing of an excessive volume of material, or, in the event that thesubstrate and/or pump is in motion, leading to dispensing of material atan undesired location on the substrate.

The present invention mitigates or eliminates the likelihood oferroneous dispensing by suspending the flow of material in the materialflow path. This suspension of material flow can, in one embodiment, takethe form of a reverse suction, or siphon, that is applied to thematerial flow path. In another embodiment, prevention of the forwardflow of material at the dispense tip can be achieved by suspending thematerial in place in a manner that not require outright reverse suctionor siphon of the material flow path, but rather prevents forward flow ofmaterial, for example, by reducing the applied positive pressure, or byconstricting the fluid path. In either case, such action results insuspension of the forward flow of material, and, if desired, mayoptionally cause an inward draw of the material 422 at the outlet of thedispense tip, as shown in FIG. 18B.

In one example, material suspension is accomplished by applying anegative pressure, for example −1 psi, to the volume 440 above theplunger 410 (see FIG. 17). For example, a vacuum 406 can be drawn on theplunger by the air pressure/vacuum unit 402 to oppose its furthermovement in a downward direction. Because the system is substantiallysealed from ambient air between the plunger 410 and the outlet of thedispense tip 82, the evacuation of the air, the force of which operateson the plunger 410, is translated to the material at the outlet of thedispense tip 82, which, in turn suspends the material, or, optionally,draws the material in a reverse direction. In either case, theinadvertent dispensing of material is prevented. In general, thestronger the applied negative pressure, the stronger the inward draw ofthe material at the outlet port 82. Depending on the viscosity of thematerial, suspension of the material may be achieved by reducing theamount of applied positive pressure, rather than by applying negativepressure.

In some cases, depending on the viscosity or surface tension of thematerial, for example in the case of a self-leveling, low-viscositymaterial, a plunger is not needed for applying the positive and/ornegative pressure to the material. In this case, positive and/ornegative pressure is applied directly to the upper surface of thematerial, and a plunger is not used.

In another example, forward material flow, and therefore inadvertentdispensing of material, can be prevented by constricting material path,for example at the feed tube 40. With reference to FIGS. 19A and 19B,assuming the feed tube 40 to be formed of an elastically compressiblematerial, single, or multiple rollers or pinchers 451 are adapted forinward and outward movement. During a dispensing operation, the rollers451 are spaced apart, and allow material 436 to freely flow through thefeed tube 40. Following the dispensing operation, the rollers 451 moveinward relative to each other, constricting the feed tube, and thereforeclosing off the introduction of material 436. Assuming a substantiallysealed material path, between the rollers 451 and the dispense tipoutlet 82, as described above, the pinching of the feed tube 40 in thismanner results in suspension of the material at the outlet 82.

In an alternative embodiment, mechanical means may be provided forapplying downward or upward pressure on the plunger, as needed, in orderto induce material flow and material suspension.

As an alternative to, or in addition to, suspension of the material flowpath to prevent inadvertent dispensing, the pump motor 42 (see FIG. 1A),which normally operates to rotate the auger screw in a first direction,for example a clockwise direction 408, during a dispensing operation,can be made to counter-rotate in a second, reverse, direction, forexample in a counterclockwise direction 409 for a predetermined lengthof time. In this manner, a reverse pumping motion is placed on the fluidpath, causing the fluid to be drawn in an upward direction, as shown inFIG. 18B. With the reverse pumping motion, the material is suspended, ordrawn inward, as described above. Since the material path is sealed bythe O-ring 412, ambient air does not compromise the material suspension,and therefore, the material is prevented from being inadvertentlydispensed at the outlet 82.

In a preferred embodiment, both operations are performed to enhance theresulting suspension of the dispensed material. For example, asuspension, or a negative pressure, is placed on the material path and areverse motion is imparted on the auger screw. The operations may beperformed simultaneously, or subsequent to one another, depending on theapplication.

The use of a closed-loop servo motor, as described above, allows forenhanced control over the operation of the reverse rotation imparted onthe auger screw. For example, the speed and acceleration of the augercan be controlled, as described above, to enhance the suspension orsiphoning action. This, in combination with the dispensing controllerdescribed above for timing the operation of the motor and airpressure/vacuum unit, provides a system and method that mitigates orprevents unwanted release of fluid at the dispense tip following adispensing operation, or between subsequent dispensing operations.

At the start of the next dispensing operation, the negativepressure-induced, or otherwise-induced suspension of the material, isremoved, positive pressure is applied, and the motor resumes rotation inthe positive direction. During the previous cycle, assuming that themotor was used to impart reverse motion on the feed screw, as describedabove, the number of counts of reverse motion are retained, and themotor is preferably returned to its original position prior to resumingmotion in the positive direction.

While this invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and detail may bemade herein without departing from the spirit and scope of the inventionas defined by the appended claims.

For example, the enhanced control over material flow offered by thevarious configurations of the present invention make the pump system ofthe present invention especially amenable to use with dispense needleshaving a flat dispensing surface with a cross pattern formed in thedispensing surface for dispensing cross patterns for providing a filletsfor boding a die to a substrate. Particularly, since the closed-loopservo motor pump of the present invention offers control over bothposition and velocity of the feed screw, the delivery of fluid throughthe needle to the cross pattern can be controlled to a level ofprecision previously unattainable. Cross-pattern-style fillets can beachieved at a level of accuracy orders of magnitude beyond thosecurrently achieved.

In addition, although the exemplary mechanisms described above forplacing the material in suspension include applying reverse pressure tothe reservoir, pinching the feed tube, and reversing the direction ofthe motor, other mechanisms capable of placing the material undersuspension are equally applicable to the present invention.

I claim:
 1. A material dispensing pump comprising: a closed-loopservo-motor having indexed rotational positions; a dispensing controllerthat generates control signals to control the servo-motor, wherein theservo-motor performs a dispensing operation in response to the controlsignals; a housing having an opening; a removable cartridge assemblypositioned in the opening, the cartridge assembly having a cavity, aninlet port, an outlet port in communication with the cavity, and a feedmechanism extending through the cavity, the feed mechanism including acylindrical neck and a feed path, the feed path being substantiallysealed from ambient air between the inlet port and the outlet port by aseal positioned about the neck between the neck and the cartridgeassembly and a securing device that secures the seal in position aboutthe neck, wherein the seal substantially seals the feed path fromambient air, the closed-loop servo-motor driving the feed mechanism in afirst direction of rotation during the dispensing operation and a seconddirection of rotation opposite the first direction, wherein the movementof the screw in the second direction operates to further place materialin the feed path to be presented to the inlet port in suspension.
 2. Thematerial dispensing pump of claim 1, wherein the control signals controlat least one of the rotational position, the angular velocity, and theangular acceleration of the servo-motor during the dispensing operation.3. The material dispensing pump of claim 1 further comprising a positioncontroller that controls the position of the pump relative to asubstrate.
 4. The material dispensing pump of claim 3, wherein theposition controller operates in conjunction with the dispensingcontroller, wherein when the position controller generates a time-basedsignal to the dispensing controller, the dispensing controller initiatesthe dispensing operation in response to the time-based signal bygenerating a control signal to control the feed mechanism based on theindexed rotational positions.
 5. The material dispensing pump of claim 1further comprising a material reservoir in communication with the inletport, the material reservoir containing the material to be dispensedduring the dispensing operation.
 6. The material dispensing pump ofclaim 5 further comprising a feed tube coupled between the materialreservoir and the inlet port.
 7. The material dispensing pump of claim 6wherein the feed tube comprises an elastically compressible material andwherein the material dispensing pump comprises means for constrictingthe feed tube to place the material in suspension.
 8. The materialdispensing pump of claim 5, wherein the material reservoir comprises asyringe and wherein positive pressure is applied to the material in thesyringe.
 9. The material dispensing pump of claim 8, wherein thematerial suspension unit applies a negative pressure to the materialfollowing the dispensing operation to place the material in thesubstantially sealed feed path in suspension.
 10. The materialdispensing pump of claim 9, further comprising a pressure unit, whereinthe negative pressure comprises a vacuum provided by the pressure unitand drawn on the material in the syringe.
 11. The material dispensingpump of claim 9, wherein the negative pressure comprises a vacuum drawnon the material in the syringe.
 12. The material dispensing pump ofclaim 8, wherein the positive pressure comprises pumped air applied tothe material in the syringe.
 13. The material dispensing pump of claim1, wherein the seal includes an O-ring.
 14. The material dispensing pumpof claim 1, wherein the securing device includes a threaded spanner nutthat applies pressure in a direction along a longitudinal axis of thefeed screw that compresses the seal about the neck of the feed screw.15. The material dispensing pump of claim 1, wherein the cartridgefurther comprises a recessed pin capture that receives a pin on acorresponding material dispensing pump housing for securing thecartridge to the material dispensing pump.
 16. The material dispensingpump of claim 1, further comprising a pin capture that comprises a holeand wherein the cartridge is a fixed-z type cartridge.
 17. The materialdispensing pump of claim 16, wherein the pin capture comprises anelongated groove and wherein the cartridge is a floating-z typecartridge.
 18. A method for dispensing material, comprising: controllinga servo-motor by generating, from a dispensing controller, one or morecontrol signals; performing, by the servo-motor, a dispensing operationin response to the control signals; and positioning a removablecartridge assembly in an opening of a housing of a material dispensingpump, the cartridge assembly having a cavity, an inlet port, an outletport in communication with the cavity, and a feed mechanism extendingthrough the cavity, the feed mechanism including a cylindrical neck anda feed path, the feed mechanism positioned such that the feed path issubstantially sealed from ambient air by positioning a seal about theneck between the neck and the cartridge assembly and providing asecuring device that applies pressure in a direction along alongitudinal axis of the feed mechanism and that positions the sealabout the neck, wherein the seal substantially seals the feed path fromambient air; and during the dispensing operation: driving the feedmechanism with the closed-loop servo-motor in a first direction ofrotation; and, following the dispensing operation, driving the feedmechanism with the closed-loop servo-motor in a second direction ofrotation opposite the first direction, wherein the movement of the screwin the second direction operates to further place material in the feedpath in suspension.
 19. The method of claim 18, wherein the material inthe feed path is placed in suspension by applying negative pressure tothe material.
 20. The method of claim 18 further comprising controllingthe position of the pump relative to a substrate during the dispensingoperation, wherein controlling the position of the pump is synchronizedwith controlling a rotational position, an angular velocity, and anangular acceleration of the servo-motor.
 21. The method of claim 18further comprising providing the material from a material reservoir incommunication with the feed path, the material reservoir containing thematerial to be dispensed during the dispensing operation.
 22. The methodof claim 21 further comprising coupling an elastically compressible feedtube between the material reservoir and the feed path, and constrictingthe feed tube to suspend the flow of material.
 23. The method of claim18 further comprising controlling a rotational position, an angularvelocity, and an angular acceleration of the servo-motor during thedispensing operation.